1). Field of the Invention
Embodiments of this invention relate to a method and apparatus for producing electromagnetic radiation, particularly for use in semiconductor substrate processing.
2). Discussion of Related Art
Integrated circuits are formed on semiconductor wafers. The wafers are then sawed (or “singulated” or “diced”) into microelectronic dice, also known as semiconductor chips, with each chip carrying a respective integrated circuit. Each semiconductor chip is then mounted to a package, or carrier, substrate. Often the packages are then mounted to a motherboard, which may then be installed into a computing system.
Numerous steps may be involved in the creation of the integrated circuits, such as the formation and etching of various semiconductor, insulator, and conductive layers. Before the various layers may be etched, a layer of light-sensitive photoresist is formed on the substrate to protect the portions of the substrate that are not to be etched.
Machines referred to as photolithography steppers are used to expose the desired pattern in the photoresist layer. In order to achieve the desired pattern, light, or electromagnetic radiation, is directed through a reticle, or “mask,” and focused onto the substrate.
As the features on the semiconductor substrates become smaller, shorter wavelength electromagnetic radiation is required to expose the photoresist. One form of such electromagnetic radiation is known as “extreme ultraviolet” (EUV) light. EUV light is often produced in plasma chambers by applying a voltage across a cathode and an anode, which are held within a plasma emission gas, such as xenon.
As the plasma is generated between the cathode and anode, tremendous heat often builds up on the anode, which can lead to the anode becoming permanently damaged, such as by melting.